Aliphatic polyesters, such as polyglycolic acid and polylactic acid, have called attention as biodegradable polymer materials giving little load to the environment as they are decomposed by microorganism or enzyme present in nature, such as soil and sea water. Particularly, polyglycolic acid has excellent initial strength, degradability and absorptivity in bodies and is therefore utilized also as a medical polymer material for is surgical suture, artificial skin, etc.
For such use wherein the initial strength and biodegradability of polyglycolic acid resin are positively utilized, it is desired to control the initial strength and biodegradability at a high accuracy. As for the molecular weight directly governing the initial strength, the present inventors, et al., have found it possible to well control the molecular weight of polyglycolic acid resin by subjecting glycolide (cyclic ester) containing proton-source compounds inclusive of water and alcohol as initiators and molecular weight-adjusting agents based on a total proton concentration and a ratio (carboxylic acid/ester mol ratio) between a mol concentration of carboxyl (carboxylic acid)-source compounds including water and a mol concentration of alkoxy carbonyl (ester)-source compounds, as polymerization-controlling indexes, whereby a process for producing an aliphatic polyester has been proposed (Patent document 1 listed below). On the other hand, as for the biodegradability, there are individually known that it correlates directly with hydrolyzability and the hydrolyzability of an aliphatic polyester correlates with a terminal carboxyl concentration (Patent document 2 below) and that it correlates with a residual glycolide content (Patent document 3 below). However, there has not been a method of controlling the moisture resistance by considering the contribution of both terminal carboxyl group concentration and residual glycolide content.
Patent document 1: WO2005/044894A
Patent document 2: JP2001-261797A
Patent document 3: WO2005/090438A